Conventionally, there is known an art of using “peak shift” that effectively utilizes electricity of nighttime during which electricity use is generally small and electricity rate is low, in order to realize reduction in electricity rate and equalization of load of electricity demand.
For example, as for an electronic device drivable by a battery, there is known a technique that the battery is charged by automatically feeding electricity to the battery from an AC (alternating current) power source in a predetermined nighttime, and the battery and the AC power source are automatically switched over to function as a driving power source of the electronic device according to predetermined times during which the AC power source and the battery are respectively usable (e.g., see Japanese Patent Application Laid-open No. 2000-29576).
Also known is a technique that such an electronic device is scheduled to be used under driving by a battery is determined, and when the electronic device is scheduled to be used under battery driving, the battery is charged by feeding electricity to the battery by using the AC power source even if the present time falls within the time during which use of AC power source is prohibited (e.g., see Japanese Patent Application Laid-open No. 2005-25382).
In the network system in which such an electronic device is connected with a feeding hub by using a network cable, also known is a technique that each electronic device instructs priority of feed need to the feeding hub, and the electricity feeding is conducted for each electronic device according to the instructed priority (e.g., see Japanese Patent Application Laid-open No. 2007-288401).
However, in a conventional feeding technique for an electronic device which is drivable by a battery, when an amount of charge of the battery of the electronic device runs short in daytime, the electronic device is charged from an AC power source, however, since the electricity rate of AC power source in daytime is high, the electricity rate will not be reduced, and the load of electricity demand is not equalized.
Furthermore, even when a setting is made to use a battery and not to use AC power source in daytime during which a predetermined battery is usable, the electronic device has to use AC power source of high electricity rate when the battery runs short in daytime during which electricity rate of AC power source is high, so that the electricity rate is not reduced, and load of electricity demand is not equalized.
When there is a schedule that the electronic device is used by battery driving, it is necessary to use AC power source of high electricity rate even when the current time is a daytime during which use of AC power source is prohibited, so that the electricity rate is not reduced, and load of electricity demand is not equalized.